ASK DOCTOR K: Genes aren't necessarily predictors of Alzheimer's

DEAR DOCTOR K: Alzheimer's runs in my family. Will it help to get gene testing for this disease?

DEAR READER: Family history is indeed a risk factor for Alzheimer's. If you have a parent or sibling with Alzheimer's, you're more likely to develop the disease than someone who does not have a close relative with this condition.

Genetics is most important in families with a history of early-onset Alzheimer's (occurring between ages 30 and 60). The early-onset form accounts for less than 1 percent of all Alzheimer's cases, but in most people with early-onset disease, the cause is one of several altered, or mutated, genes that the person has inherited from a parent.

Several genes responsible for early-onset Alzheimer's have been identified. They are called APP, PSEN1 and PSEN2. If someone inherits one of these mutated genes, it is very likely (but not certain) he or she will develop the disease.

Testing for these genes is costly and is not usually covered by insurance. At this time, there is no treatment proven to prevent or slow the onset of Alzheimer's disease. However, some people want to know if they have one of these genes so they can use that information in planning for their future.

If one of my parents had developed early-onset Alzheimer's, I would have wanted to know if I had inherited the gene. If so, I might have planned my career and my non-professional life differently. Fortunately, my parents did not develop this disease.

You also may choose to be tested. For you, like me, perhaps bad news is better than living with uncertainty. Or you may want the opportunity to enroll in trials for experimental treatments.

Everything I've said so far applies only to early-onset Alzheimer's disease. Most cases of the disease start after age 60. We know of just one gene that is a reasonably strong predictor of this more typical form of Alzheimer's: APOE. People who inherit two copies of the APOE4 type of the APOE gene are at much higher risk for developing Alzheimer's compared with people who have no copies of the gene.

However, most authorities do not recommend getting tested for the APOE4 gene. That's because the gene does not provide a solid answer. If you inherit two copies of the gene, you may still avoid Alzheimer's. And if you inherit no copies, you may still get it. Nevertheless, some people want to know if they are at increased risk. I have not had myself tested for this gene.

Human genetics has developed enormously in the past 30 years. In the 1980s, few scientists imagined that we would discover the structure of every human gene in their lifetime, or even their children's lifetime. But we have. And we have identified thousands of genes that are linked to particular diseases.

However, this information has not yet led to many highly accurate predictions of what diseases a person is at high risk for, or to many cures. I'll explain why in another column.